If you have a STEREO file with only one MONO source on one of the channels and not the other, you'd probably be best off to covert the file into a TRUE MONO wav file that has only the one channel on it. Right now you're file is twice as large as it needs to be, and if you simply copy the contents of that channel to the other channel, it'll remain twice as big as it needs to be. If it is saved as a true mono file, most (maybe not all, but I have yet run into a player that doesn't do this) players will simply play the mono file through both speakers. Now, if you're burning a CD, that's a different story. Then you should copy it to the other channel and leave the file in stereo format. I do this sometimes b/c I run my R4 in 2s Stereo mode usually, so if I only take a single feed from the SBD, I end up with a stereo file with sound only in one channel. Usually, I do this: I convert that file to true mono, so my original wav is half the size of the stereo wav that was recorded. I FLAC that and keep it forever as my original. Then I edit and render out a stereo version of the file (which is really just the same source in both channels), dither/resample to 16 bit / 44.1, track it, flac it, and share it from there. Point is, there are mono wav files and there are stereo sound files, but you can still have a mono recording in both channels of a stereo file. Also, this is true with MP3s too. If you encode a true mono wav file into a true mono MP3 file, it'll be much smaller, but your ipod and such will still play the mono file through both speakers cause it knows it's mono. But if your mono track is stuck in one channel of a stereo file, then the ipod will only play it through the one side. Did that make sense?